The present invention relates to a frequency drop out compensating circuit and method thereof in an optical disk system, and more particularly to a frequency drop out compensating circuit and method thereof which can be applied to the signals of both NTSC (National Television System Committee) and PAL (Phase Alternation by Line) systems.
In general, an optical disk system such as a laser disk has been well regarded as an apparatus for recording large quantities of information due to many advantages. The optical disk system enables audio and video signals to be recorded at a high density and then reproduced, while exhibiting a much better random access function than other recording systems for audio/video data. Also, due to the use of a reflected laser beam for reading the signal to be reproduced, neither the disk nor pickup head becomes worn because they have no contact with each other.
However, such a laser disk system has a disadvantage in that signal errors or a temporary fall in output level may occur due to minor defects, dust or bugs in the recording medium, i.e., the optical disk.
Therefore, the optical disk system adopts one of two methods for the compensation of drop out. There are an amplitude drop out compensating method and a frequency drop out compensating method. The amplitude drop out compensating method is mainly to compensate an abrupt decrease of the level of an input FM signal due to the imperfections in the reproduced signal caused by damage to the disk or by a bug in the system. The frequency drop out compensating method compensates for deviation in the frequency of an input FM signal due to the partial loss of data by disk corrosion or a disk defect, which is generated during manufacturing.
The frequency drop out compensating method is not compatible with the different types of broadcasting systems and therefore different compensating circuits are used depending on the television broadcasting systems used. For example, the frequency drop out compensating circuit used for NTSC systems can compensate for frequency drop out in the NTSC system but cannot compensate for frequency drop out in other broadcasting systems.
Therefore, for an optical disk system which is used with both NTSC and PAL systems, separate frequency drop out compensating circuits (one for NTSC and one for PAL) have had to be provided and selectively switched into use. Thus, the circuit-configuration is more complex and the cost is higher.